Regulatory Matters - Retail Rate Case Filing (Details) - Retail Rate Case Filing with Arizona Corporation Commission - ACC - APS	Apr. 22, 2019 USD ($)	Jan. 03, 2018 Customer	Nov. 13, 2017 USD ($)	Mar. 27, 2017 USD ($) $ / kWh	Mar. 26, 2017 $ / kWh	Mar. 31, 2019 appeal
Public Utilities, General Disclosures [Line Items]
Approximate percentage of increase in average customer bill				3.28%
Approximate percentage of increase in average residential customer bill		4.54%		4.54%
Net retail base rate, increase				$ 94,600,000
Non-fuel and non-depreciation base rate, increase				87,200,000
Fuel-related base rate decrease				53,600,000
Base rate increase, changes in depreciation schedules				$ 61,000,000.0
Authorized return on common equity (as a percent)				10.00%
Percentage of debt in capital structure				44.20%
Percentage of common equity in capital structure				55.80%
Rate matter, environmental surcharge cap rate (in dollars per kWh) | $ / kWh				0.00050	0.00016
Rate matter, resource comparison proxy for exported energy (in dollars per kWh) | $ / kWh				0.129
Periodic metering infrastructure opt-out fee			$ 5
Number of appeals | appeal						2
Number of customers named in complaint | Customer		25
AZ Sun Program Phase 2
Public Utilities, General Disclosures [Line Items]
Public utilities, minimum annual renewable energy standard and tariff				$ 10,000,000
Public utilities, maximum annual renewable energy standard and tariff				$ 15,000,000
Subsequent Event
Public Utilities, General Disclosures [Line Items]
Public utilities, rate matters, demand side management adjustor charge	$ 5,000,000